Tetracycline antibiotics and their salts are well-known therapeutic materials. It has been proposed in the prior art to employ solutions of such tetracycline antibiotics as topical therapeutics for the treatment of various disorders, such as acne vulgaris. Tetracycline antibiotics are known to degrade to form epitetracycline, anhydrotetracycline, epianhydrotetracycline and other degradation products, some of which are unidentified. These degradation products have negligible therapeutic activity. This degradation appears to increase when solutions of tetracycline antibiotics are employed. Solutions of neutral tetracyclines in nonaqueous solvents are disclosed in U.S. Pat. Nos. 3,219,529 and 3,389,174. These references, however, do not disclose or suggest stable nonaqueous solutions of tetracycline antibiotic salts. In fact, these references specifically state that they are not concerned with such salts. An aqueous ethanol solution of tetracycline hydrochloride has been commercially marketed under the tradename "Topicycline", but it is relatively unstable in its solution form.
There is thus a need for a stable nonaqueous solution of tetracycline antibiotic salts.